What we found

We charged the batteries, then ran them flat – and we repeated this until they stopped working. This is similar to using them constantly in a kid's remote-controlled car (although some of the batteries may last longer under a lighter load). We measured their performance at the start and end of the test. We also tested the batteries for "self-discharge" – this showed how well they kept their charge when they weren't being used.

Performance

The Energizer Recharge had one of the longest average running-times between charges.

The claimed capacity of ready-to-use rechargeable batteries in our test was between 2000 and 2100mAh; most of the standard rechargeables claimed a capacity between 2450 and  2600 mAh (see "What's a mAh?" below). We found the claims to be close enough … but the Powertech, Vapex and Varta Power Accu standard rechargeables all claimed a capacity that was more than 16 percent higher than their measured capacity.

Four of the five batteries we recommend are ready-to-use: Kodak, Sanyo Eneloop, Varta Ready2Use and Sony. The fifth recommended battery is the Eveready standard rechargeable. These batteries all performed very well: they ran for at least 109 minutes between charges and were still recharging after 200 uses.

At 138 minutes, the Energizer Recharge standard rechargeable had one of the longest average running-times between charges and could be recharged 105 times. It was also the most consistent performer, losing only 21 percent of its running-time by the end of its life. If a long running-time between charges is important to you, this battery is worth considering. The downside is that it won't last for as many recharging cycles as the lower-capacity batteries we recommend.

All the batteries we tested lost some of their charge when stored unused – most lost between 15 to 20 percent over the 12-week test period. The exception was the Varta Power Accu, which lost over 40 percent of its charge. Apart from this battery, there wasn't much difference in self-discharge between the ready-to-use and standard rechargeables. This surprised us, because the manufacturers claim that ready-to-use batteries hang on to their charge for longer when not being used. Even the best battery at resisting self-discharge – the ready-to-use Duracell Active Charge – lost 13 percent of its charge when stored unused.

Price

The batteries in our test cost between $18 and $30 for a four-pack. Packs that include a charger are typically priced between $30 and $80. A four-pack of equivalent disposable alkaline batteries (Energizer Max) costs around $10. All the rechargeable batteries in our test cost more initially – but they last for at least 50 charges, so it's not long before they've paid for themselves.

Ready-to-use

Standard NiMh rechargeable batteries lose their charge if they’re not being used. Ready-to-use rechargeables that aren’t being used claim to hold on to their charge for longer, which means they shouldn't need charging when you buy them. They could also be handy for devices which aren't frequently used.

What's a milliamp-hour (mAh)?

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Battery capacity is measured in milliamp-hours (mAh). This is a measure of how long a battery will last before it needs to be recharged or disposed of. The higher its mAh rating, the longer it should last. For example, a 2000 mAh battery should last for 8 hours in a gadget which draws 250 milliamps.